Colon

 

There are two main functions of the colon

  • Absorption of water from chyme which then makes chyme semi solid and converts it into fecal matter
  • Storage of chyme/fecal matter until it can be expelled.

Even though movement in the colon is sluggish, it is still available to provide peristaltic movement which can be divided into two main types as in the small intestine

  • Mixing movement which helps to mix food/chyme
  • Propulsive movement which helps to move chyme forward. In the ascending colon it is still fluid; in the transverse colon it becomes mush while in the descending colon it turns into semi solid.

Haustrations, just like segmentation in the small intestine, helps the propulsion of material in the colon. They are formed by longitudinal muscles (called teniae coli) ) of the colon which shortens the length of the colon and by circular muscles which constrict the colon almost to occlusion. The combination of the two actions is almost like milking the colon in order to move the contained fecal matter towards the rectum and anus.

Mass movements

Despite the slow and steady movement of chyme which later becomes converted into fecal matter in the colon, the colon develops mass movement in which haustrations are eliminated and the entire colon contracts in the transverse  colon thereby propelling mass of feces towards the rectum. It leads to the feeling of defecation. Gastrocolic and duoenoclic reflexes affect these mass movements to also influence defecation, just like irritation in the colon as in ulcerative colitis.

Secretions

Crypts are also in abundance in colon (check histology)as in small intestine but they are not provided with villi. The enterocytes of the colon do not secrete enzymes for food digestion; rather they produce copious amounts of mucus. Colon produces large amounts of mucus in response to bacterial or other infectious agents, which then helps to dilute the noxious material and cause mass movement to remove the infectious agents in defecation, with fecal matter.

 

 

 

 

 

 

 

 

 

       


Cross section through colon low power

 

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